Recently, methicillin resistant Staphylococcus aureus (hereinafter designates as MRSA) has become a social problem as a major causative microorganism of hospital-acquired infection. This pathogenic microorganism is resistant to various medicines such as β-lactam antibiotic, and antibiotics such as glycopeptide antibiotic vancomycin and aminoglycoside antibiotic arbekacin, which are reported at present to exhibit almost no resistance, are generally used for treatment of MRSA. In addition to this, combination therapy of β-lactam antibiotics or that of β-lactam antibiotic and other antibiotic having different active site is employed at present (Yoshimi Hasegawa et al. “Science of antibiotic administration”, p. 264-273, 1998).
Resistant strains against vancomycin and arbekacin have already appeared. It has become a problem that these antibiotics have been known to have adverse reaction to exhibit hearing impairment caused by eight cranial nerve disorder. In order to cope with these problems, a substance having an action for recovering effect of β-lactam antibiotic has been reported to date. For example, tea extract or active fraction thereof showing synergistic effect by using in combination with antimicrobial agent including βlactam antibiotic are agree with that (JP-A-9-509677). Since novel stemphones have an action for enhancing antimicrobial activity of imipenem, which belongs to carbapenem in β-lactam antibiotic, and at the same time have the action for enhancing antimicrobial activity of cloxacillin in penam as well as cefazoline in cephem, it is expected to apply for the combination therapy with antimicrobial agents including β-lactam antibiotic. Novel stemphones are clearly distinguished from the polyphenol compounds, which are the active ingredients of the tea extract or the active fraction thereof, in their molecular formulae and chemical structures.